The present invention relates to a valve closure gate assembly for a foundry ladle comprising two mutually slidable closure gates with respective outlet openings for regulating the flow of melts.
At the present, foundry ladles with stopper rods or valve closure gates are used in steel and foundry plants. The material of which these closure elements are made should have physical and chemical properties to reliably resist high temperatures, thermal shock stresses, and the corrosive effects of molten metals and slags. The interface of contact surfaces of the gates of the valve closure gate assemblies should also prevent the leakage of melt, if the foundry ladle is closed, and their surface should be resistant to wear during multiple openings and closings.
In view of the above-mentioned requirements, application of the valve closure gates has increased recently as a consequence of their advantages in comparison to the system of stopper rods. The closure gates of valve closure gate assemblies manufactured from ceramic materials are suitable from the view of heat resistance, but the sealing surfaces of the valve closure gates become abraded and roughened during operation by the combined abrasive and corrosive action of melt and slag, thereby losing their sealing characteristics. The outlet openings are also gradually worn by the action of melt and their enlargement undesirably affects the casting process.
The above-mentioned difficulties are recently solved by manufacturing the fundamental body of the closure gate of the valve closure gate assembly from common ceramic materials, which have relatively lower melting temperatures, and by furnishing the surfaces exposed to the direct action of melt with resistant surface layers from refractory materials with suitable properties in respect to their resistance against the abrasive and corrosive action of melts. These materials are used for manufacturing the linings of flat sealing surfaces of the closure gates and serve also for lining the outlet openings, either directly or by means of connecting interlayers. The closure gates of the valve closure gate assemblies made in this way have the advantage of longer service life and greater tightness of closure in comparison to the original gates with an unprotected surface. However, their disadvantage consists in a low durability of bonds between both ceramic parts because the connection interlayer cracks due to the different heat expansions of the materials used. The difficulties occur also with surface layers applied by the technology of plasma or heat spraying, particularly in the application of this layer on the inner wall of the outlet opening.